Argument Type:

ClickData 

Description:

This method is called whenever a button or hotkey containing a script function is run. The ClickData object provides useful information about the command environment, including source and destination tabs and paths, any selected files, command line arguments, any qualifier keys that were held down, etc. This information is all accessible from the ClickData.func property (which returns a Func object).
 

Note that when a script function is run, any instructions not contained inside a function are executed first, before OnClick is invoked. This means that the OnClick method is technically optional (as you could just implement the entire script outside of a function), although it is recommended that you implement it simply for the benefit of the ClickData object it receives.